The top military commander of Syria's rebranded Al-Qaeda offshoot was killed in an air strike that targeted a meeting of the group's leaders, rebel sources say.

The Fateh al-Sham Front, formerly known as the Al-Nusra Front, announced on Twitter that commander Abu Omar Saraqeb was "martyred" in the countryside of Aleppo, where the group has been playing an instrumental role in ongoing battles against the Syrian Army and Iranian-backed Shi'ite militias.

The group is part of the Army of Conquest which is the largest and most effective rebel alliance in Syria.

The Syrian Observatory for Human Rights confirmed that air strikes killed Saraqeb as well as another rebel commander it identified as Abu Muslem al-Shamid.

The Al-Nusra Front announced in July it had changed its name and ended its relationship with Al-Qaeda, but the change was dismissed as cosmetic by both Washington and Moscow, which still view the group as a terrorist organization and have targeted it for air strikes.

It was not clear whose air strikes killed the Nusra commanders, whether Russian, U.S., or Syrian.